Most internal combustion engines in use today run on either gasoline or diesel fuel. The cost of such fuels has made engines that run on compressed natural gas (CNG) attractive for those who use their vehicles extensively as well as have access to a supply of CNG. Converting a diesel engine to run on compressed natural gas requires decreasing the compression ratio of the engine, as well as providing a way to install a spark plug (most diesel engines ignite the fuel/air mixture using compression of the fuel rather than a spark plug). Many methods of accomplishing these goals require permanent modification of the engine components through machining. Thus, a simplified method of increasing the compression ratio while providing a means of installing a spark plug, without permanent modification of the engine, is desired.
Due to the sporadic availability of CNG, as well as the fact that, depending on engine temperature, CNG may not always be the optimal fuel choice, it would be desirable to have an engine that could selectively utilize one of a plurality of different fuels is desirable. The ability to select the desired fuel manually, through a microcontroller based on information about engine operating conditions, or both, would increase the likelihood of an optimal fuel being selected for a give set of driving conditions.